Portable sound suppressor for aircraft jet engines



Oct. 25, 1960 c. J. MORGAN 2,957,537

PORTAB LE SOUND SUPPRESSOR FOR AIRCRAFT JET ENGINES Filed May 16, 1958 INVENTOR CONRAD J MORGAN ATTORNEY United States Patent M PORTABLE SOUND SUPPRESSOR FOR AIRCRAFT JET ENGINES Conrad J. Morgan, 7 Tanglewood Circle, Reading, Mass. Filed May 16, 1958, Ser. No. 735,910

3 Claims. (Cl. 181-56) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a method of and apparatus for reducing the noise and heat of the exhaust from jet engines while being operated on the ground and more particularly to a method and apparatus for reducing the noise and heat of the exhaust from jet engines fllithout the use of large sound chambers, water and the '1 e.

It has been the practice to suppress the noise and heat of jet engine exhaust by the use of towers, water-spray tunnels and baffles. These devices are of such great size and bulk that their transportation from place to place is prohibitive. They are also restricted in their use with engines which are installed in aircraft and in portable test beds. Moreover, the large size of the above devices make them impractical as a part of a squadrons equipment.

Furthermore, the gas discharged from jet propulsion motors is usually at an extremely high temperature and conventional silencing means are likely to deteriorate rapidly under such conditions.

An object of the present invention is the provision of a method and apparatus for suppressing the noise and heat of the exhaust from jet engines while said engines are being operated on the ground.

Another object of the invention is the cooling of the discharge gases so that they will not destroy the means provided for silencing them.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

The single figure shows a cross-sectional view of a sound suppressor attached to the exhaust end of a jet engine.

Referring now to the drawing there is shown a sound suppressor 10 attached to the exhaust end of a jet engine 11. The jet engine sound suppressor is comprised of a frusto-conical shaped housing with increasing diameter formed by an outer shell 12 and a surface of a spherical segment forming a large concave reflector 13. Attached to the outer periphery of the reflector 13 is a sound chamber 14 the purpose of which is to be described hereinafter. Within the sound suppressor 10 is a series of nozzles 15, said nozzles being formed by annular-shaped nozzle dividers 20 mounted by brackets (not shown) on shell 12. Each of the nozzle dividers is different in crosssectional area, said section being taken through the longitudinal axis of shell 12 and said longitudinal axis lying within the sectional plane, and shaped so as to provide a different size nozzle between each of said dividers. The nozzles decrease in size as their distance from the intake end increases and are concentric with the horizontal axis of the sound suppressor. The smallest di- 2,957,537 Patented Oct. 25, 1960 Yider 21 has a plug center about which is mounted a series of whistles 22. The whistles are so arranged that the sound waves radiate in a plane normal to the longitudinal axis of the sound suppressor housing 12. As stated above, the nozzles have different configurations so that the sound emanating from each of said nozzles will be of a different pitch. Located aft of the exhaust opening 11 and in line with said opening there is mounted a sound reflector 13 which reflects the sound waves back towards the nozzles. The outer shell 12 having a constantly increasing diameter, the maximum diameter reached at the reflector 13 is such as to enable the suppressor 10 to handle the volume of the exhaust at or near atmospheric pressure. The reflector 13 is sufficiently large to eliminate substantially all of the sound waves emerging from the nozzles. However, a small concave reflector 23, having its concave surface facing the concave surface of reflector 13, is provided to concentrate the remaining sound waves and which in turn directs the sound Waves into a sound absorbing chamber 14, Where the wave-free exhaust gas may be emitted through exit 25.

The sound suppressor described above operates in the following manner: The hot exhaust gases of the jet engine are directed through the series of nozzles 15, each nozzle taking off the outer layer of hot gases. As the gas passes through each nozzle, it is expanded to near atmospheric pressure as it approaches the outer shell 12. During the expansion process, the temperature of the gas is reduced and the sound is reduced in pitch. Each of the nozzles 15 being of a somewhat different configuration, sound waves will be emitted of a different and noncompatible frequency from each of said nozzles. As the sound waves pass over the last nozzle, they encounter the wall of sound waves being emitted by the whistles 22, thus tending to destroy the sound Waves attempting to pass through the nozzles. The sound waves which finally emerge from the exhaust of the suppressor are picked up by the reflector 13 and directed back into the unit. The reflector 13 is so curved that the sound waves reflected are returned and concentrated on a reflector 23. The reflectors separate the sound waves from the air stream and from reflector 23 substantially all of the sound waves pass through a sound chamber 14, the sound chamber being filled with a sound absorbing material. Not having an air blast to carry the sound waves out of the chamber, the waves beat themselves out on the soft interior of the chamber. The exhaust gases, which are at this point near atmospheric pressure and at greatly reduced temperature and substantially free of sound waves, are then free to leave the suppressor at the exits 24 and 25.

Thus, the noise and heat created by the exhaust gas of jet engines is greatly diminished by the cooling and expansion of the gases through the use of expansion nozzles and the reduction in amplitude of sound Waves by the algebraic summation of the various frequencies. These various frequencies are set up by the various configurations of each of the nozzles and a whistle 22. Lower temperatures, a low velocity gas, and incompatible sound waves are set up by the use of the above described suppressor, thereby prohibiting the resonance of the surrounding structure and resulting in the reduction in the intensity of the sound emitted.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that Within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Apparatus for reducing the heat and noise created ing a reflector inwardly concave relative to saidvshell, a

said shell having a series of openings adjacent said reflector for permitting the escape of exhaust gases, a plurality of annular shaped dividers positioned concentrically about the longitudinal axis of said shell, each of said dividers being of a different longitudinal cross-section through said longitudinal axis and spacedfrom each other so as to form nozzles between said dividers, a small- ,er second reflector having a concave surface mounted centrally of said shell between said dividers and said first named reflector and having its concave surface facing the concave surface of said first-named reflector, whereby exhaust gases entering said apparatus will pass through said nozzles to said first reflector and deflected to said second reflector to create sounds of various frequencies and thus tend to negate jet engine noise.

2. The apparatus of claim 1 further comprising a cone-shaped divider mounted centrally of said shell between said dividers and said second namel reflector, and having a plurality of holes therein for producing a high frequency sound. V

3. Apparatus for reducing the heat and noise created by the exhaust gases of jet engines, said apparatus comprising an outer shell having an expanded surface of increasing diameter moving outwardly and formed symmetrically about a longitudinal axis, said shell forming acylindrical pipe at its smallest diameter for insertion over the exhaust pipe of an engine and bounded at its largest diameter by a spherical reflector inwardly concave relative to said shell and having a series of openings adjacent said reflector for permitting the escape of exhaust gases, a plurality of annular shaped dividers positioned concentrically about the longitudinal axis of said shell, each of said dividers being of different cross-section and spaced from each other so as to form nozzles between said dividers, a cone-shaped divider mounted centrally of the shell and having a plurality of holes therein for producing a high frequency sound, a smaller second reflector having a concave surface, mounted centrally of said shell and adjacent said cone-shaped divider, said second reflector having its concave surface facing the concave surface of said first-named reflector, a soundabsorbing chamber mounted on the exterior convex side of said first-named reflector, whereby sound waves directed from said first reflector are deflected to said second reflector and thence to said chamber whereby the sounds emanating from an engine exhaust are substantial- 1y diminished.

References Cited in the file of this patent I UNITED-STATES PATENTS 938,101 Winters Oct. 26, 1909 s 1,685,701 Blanchard Sept. 25, 1928 2,058,932 Wilson Oct. 27, 1936 2,081,306 Rauen May 25, 1937 2,512,823 Blundell June 27, 1950 FOREIGN PATENTS 992,706 France July 11, 1951 

